Current automatic steering systems for off-road vehicles, such as the commercially available John Deere GreenStar™ Auto Trac assisted steering system for tractors, typically require an auxiliary electro hydraulic steering control system to interact with the steering system on the vehicle. A combination of GPS system signals and signals from on-board sensors are processed to provide automatic guidance of the vehicle. An electro hydraulic valve, a steered wheel angle sensor, and steering wheel movement sensor for operator override are required to control interaction of the manual system with the automatic system. Such an automatic system takes many hours to install and requires knowledge of the steering, hydraulic, and electrical systems on the vehicle. The automatic system must be specifically adapted to the particular steering system on the vehicle. Use of the system may be limited on some vehicles, such as those with dual-path hydrostatic steering. Some types of automatic steering systems, such as shown in U.S. Pat. No. 5,234,070, require a special clutch that is disengaged during one of the steering modes. Many systems require a separate steered wheel angle sensor.
In another type of system, an electric motor with a friction drive engaging the steering wheel is supported from the steering column. Such an add-on type of unit often does not integrate well into the system, and the open friction drive arrangement presents pinch points and is subject to wear in both the friction drive and at the steering wheel. Any slip in the drive can cause instability in the steering system and adversely affect steering accuracy. The system also lacks inertial measurements or real time kinematics (RTK) features for accuracies often demanded in automatic steering applications.
There is a need for a simpler, less expensive and more easily installed automatic steering system that minimizes or eliminates substantial steering system modifications and special clutches. There is a further need for such a system which is more accurate and reliable than at least most previously available retrofit sytems and better integrates, both functionally and aesthetically, into most existing steering mechanisms.